GEOCHEMICAL SIGNATURES OF MINERALIZED MAGNETITE PIPES AND THEIR RELATIONSHIP TO THE PETROGENESIS OF THE BUSHVELD COMPLEX, SOUTH AFRICA

The Bushveld Complex of South Africa, the world’s largest layered igneous intrusion, is well-known for its deposits of PGEs, Cr and V, and a variety of magnetite structural features, including layers and proposed pipe-like bodies. These features were mapped and described based on their circular exposure at the surface, and a few have been studied in three dimensions and have a vertical, pipe-like structure. However, many of the magnetite-rich “pipes”, which occur in the Main and Upper Zones of the Bushveld Complex, have ambiguous field relationships. Proposed models to explain the formation of these structures include origins of expulsive structures, ponding, or failed layers. In addition, some “pipes” have spatial relationships to major structural features, which may represent tilted magnetite-rich layers. Several proposed pipe-structures in the eastern limb of the Upper Zone were sampled and examined texturally and geochemically for characterization and for comparison against known examples of magnetite-rich layers and pipes. Several proposed “pipe” structures, which have been sampled at Texas Tech University, have similar characteristics to magnetite layers. These similarities may be indicative of these pipe-like bodies being slump structures in which the heavy, dense magnetite ponded on top of less dense silicate mush, breaking through to create a downward-plunging structure. Geochemical and textural data from Kennedy’s Vale demonstrate that three-dimensional and pipe-like structures are known to be compositionally distinct from the magnetite layers.